The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
At present, the following methods are implemented to prevent proppant entrainment:
lattices and gravel-packed filters;
chemically binding proppants and soluble additives to these proppants to increase conductivity of the pack;
sticky agents for surface/fluid modification;
soluble materials and deformable additives;
fibers.
A device for proppant entrainment prevention and a method for installation of the said device in a subsurface formation are known. A lattice is installed in a perforated section of pipe and closes perforations. The size of meshes is selected in a way to prevent proppant entrainment and to increase production of hydrocarbons.
However, the application of an integral part of the lattice may cause the accumulation of sand or proppant near the lattice surface and consequently reduces the conductivity in this area.
A method and device for completion and providing control over sand entrainment from a subsurface formation and/or for formation fracturing and prevention of proppant entrainment in one run in known. One or more perforating shots are connected and covered with one or several nets. When shots are installed in a well and adjusted, then they are blasted to penetrate formation. Perforations holes and annulus space are isolated from the well by the lattice which is then packed with gravel. Well fluid can be under pressure before the shots detonate; as a result, the permeability grows.
However, the application of this method may be limited by relief and well structure features.
In another known method, proppant covered with a cross-linking polymer is injected to prop a fracture. Technical effect is obtained due to a) use of a polymer-covered proppant and a fluid containing a furfurol spirit's polymerizable oligomer, a catalyst containing oil-soluble, slightly watersoluble organic acid, and a compound ether of a weak organic acid to absorb water formed in the polymerization process; b) use of brine water saturated by 70% or 100% with sodium chloride as a carrying medium; c) polymer-covered proppant in a carrying fluid when the time of a polymerization catalyst addition is varied. However, the application of this method assumes the availability of expensive and difficult-to-use chemical compounds, which alongside with the applied multi-stage process, makes this process much more expensive.
In another known method, proppant grains comprising a substrate with a rubber (elastomer) coating are used to prevent entrainment of particles from a reservoir. Proppant particles could have a coating made of polymers, fiber materials and/or soluble polymer, in addition to the elastomer coating.
In another known method for subsurface formation fracturing, at least part of a fracture is filled with a propping material in the form of elongated particles with a maximum-to-minimum diameter ratio of over 5, preferable option—metal wire segments. The remaining part of the fracture is filled with a standard non-metal proppant. In this case, the conductivity of the fracture improves.
A method of subsurface formation treatment by filling a fracture with a propping material and deformable particles is known. Deformable particles could be combined with a proppant to increase conductivity of the fracture, decrease formation of fine-milled particles and/or reduce backflow of proppant. Sand can be used as fracturing material, and polystyrene divinylbenzene balls are used as deformable particles.
In another known method for propping fractures in a subsurface formation, the prevention of the proppant backflow from the fracture is implemented alongside with the fracturing operation. The method is based on the application of a fiber bundles & proppant mixture for filling the fracture when it is kept open, and thereafter the fracture is allowed to close on the fiber & proppant mixture. As per patent, the backflow of proppant is prevented through the use of fiber bundles comprising 5 to 200 individual fibers with a length of 0.8 to 2.5 mm and with a diameter of 10 to 1,000 μm.
The addition of fibers or fiber-like structures in the product could contribute to the proppant backflow reduction and simultaneously increase the proppant pack density in the fracture. Fibers also allows to diminish the migration of a fine-milled proppant in the fraction, however, does not allow to eliminate this phenomenon at all.
In one known method for monitoring over proppant entrainment from a subsurface formation, the addition of fiber materials in the fracturing mixture and in the downhole gravel-packed filter reduces the backflow of proppant and/or the formation of fine-milled crumbles in the pack; this stabilizes the packing and reduces the need for high-polymeric fluids. Glass, aramid, nylon or other natural and synthetic, organic and inorganic fibers and metal filaments are the preferred material for fibers.
There is also a known method in which a subsurface formation is treated by injecting a mixture of ordinary proppant and deformable particles in the formation. Deformable particles could be combined with the ordinary proppant to improve conductivity, decrease formation of fine-milled proppant crumbles and/or diminish the backflow of the proppant. Sand and deformable particles such as polystyrene divinylbenzene balls could be used as a propping agent. Also, this patent claims the possibility of using natural materials (nut shells, seeds, fruit kernels and processed wood) for this purpose. However, natural materials introduce additional amount of fine-milled material in the pack and, thus, decrease the conductivity.